1. Field
Embodiments of the present invention relate to avionics systems for mechanically-controlled aircraft that are configured to provide envelope protection for deterring a pilot from flying outside of acceptable flight parameter limits.
2. Related Art
All aircraft have limits on acceptable airspeed, pitch attitude, and banking angles. In some fly-by-wire controlled aircrafts, envelope protection is employed to prevent or deter a pilot from exceeding acceptable limits.
For example, Airbus has an envelope protection system employed on its fly-by-wire controlled aircrafts that provides absolute limits for airspeed, pitch attitude, and banking angles. Once a limit is reached, the envelope protection system doesn't allow the aircraft to exceed it, regardless of contrary instructions by a pilot. For the purposes of envelope protection, the airplane motion is limited through electronic control of the aerodynamic surfaces of the aircraft, independent of how far beyond that limit the pilot can physically move the yoke or control column.
A Boeing envelope protection system employed on its fly-by-wire controlled aircrafts provides a “soft barrier” at its outer limits, meaning that when the limit is reached, simulated opposing force is provided as feedback to the pilot, but the pilot can override the protections by pushing or pulling harder or clicking an override button. The Boeing fly-by-wire controlled aircrafts feature artificially generated forces for the pilot to simulate the feel of a mechanically-controlled aircraft, so the simulated opposing forces for envelope protection can be accomplished by simply modifying those artificial forces.
The envelope protection systems employed for fly-by-wire controlled aircraft are unsuited for mechanically-controlled aircrafts, because the control column or yoke of a mechanically-controlled aircraft is mechanically linked to the control surfaces of the aircraft and can not move independently of these control surfaces. Since fly-by-wire systems can actuate control surfaces independent of pilot force generation on the control column, the response applied to the control column and the corresponding response applied to the control surfaces may be modified or independently set as required for particular envelope protection limits. This is not possible on a mechanically-controlled aircraft.